Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$113.84	12.327%	$127.8731	$127.87	$127.85	$127.90
Purchase #2	$163.64	3.816%	$169.8845	$169.88	$169.90	$169.90
Purchase #3	$95.78	4.192%	$99.7951	$99.80	$99.80	$99.80
Purchase #4	$246.59	6.578%	$262.8107	$262.81	$262.80	$262.80
Purchase #5	$83.43	7.504%	$89.6906	$89.69	$89.70	$89.70
Purchase #6	$119.75	9.301%	$130.8879	$130.89	$130.90	$130.90
Purchase #7	$66.93	10.423%	$73.9061	$73.91	$73.90	$73.90
7 purchase totals =	$889.96		$954.8480	$954.85	$954.85	$954.90